1. Field of the Invention
The present invention relates to a pneumatic radial tire, and more specifically to a pneumatic radial tire in which unbalanced abrasion at blocks forming a tire tread pattern can be improved without increasing tread pattern noise and decreasing tread pattern drainage.
2. Description of the Prior Art
FIG. 1 shows an example of block pattern of a radial tire. This tire block pattern is formed of a plurality of substantially quadrate or polygonal blocks 30 arranged on a tread surface T of the tire. The block pattern is formed or partitioned by a plurality of the main circumferential grooves 10 extending in the circumferential direction of the tire substantially in parallel to each other and a plurality of transversal grooves intersecting the main circumferential grooves 10 at an inclination angle.
In the block pattern of this kind, there exists a tendency such that the transversal grooves 20 are greatly inclined with respect to the circumferential direction of the tire in order to increase the drainage and decrease the pattern noise.
Therefore, in each block 30 formed by intersections of the main circumferential grooves 10 and the transversal grooves 20, there inevitably exist acute angle corners 30a and obtuse angle corners 30b. As a result, there exists a problem in that abrasion increases near the obtuse angle corners 30b, because the rigidity is lowered near the acute angle corners 30a and therefore load should mainly be supported near the obtuse angle corners 30b.
In a high-performance radial tire having a block pattern of this kind, since the tire is often used under severe conditions such as steep start, steep stop, steep turn, etc. as compared with the ordinary tires, blocks 30, arranged near a relatively-wide main circumferential grooves 10.sub.1 located on both the side areas T.sub.S of the tread surface T are in particular subjected to a great deformation. As a result, the rigidity is markedly lowered in the areas M near the acute angle corners 30a and therefore the areas N near the obtuse angle corners 30b are subjected to heavy load as compared with the areas M near the acute angle corners 30a, so that unbalanced abrasion develops between the areas N and the areas M, and a large abrasion increases at the areas N near the obtuse angle corners 30b.